The present invention relates to the field of mechanically mounting an element to a shaft. More specifically, the invention relates to an innovative tapered sleeve system used to mount a bearing assembly or other mechanical element to a shaft.
Rotary mechanical systems include elements, such as bearings, that allow relative rotational movement between respective parts. For example, a rotary system might include a stationary housing that supports a rotating shaft via a bearing assembly. The bearing assembly is typically mounted directly to the shaft and allows for the relative rotational movement between the stationary housing and the rotating shaft.
A variety of mounting systems are known and commercially available for mounting a bearing assembly or other mechanical element to a shaft. Some of these systems make use of a tapered sleeve that fits snuggly between the outer periphery of the shaft and the inner ring of the bearing assembly. The tapered outside diameter of the sleeve engages the tapered inside diameter of the bearing assembly and causes the sleeve to enter into an interference fit with both the inner ring and the shaft. Variations of this type of arrangement may include multiple sleeves that alleviate the need for a taper either on the shaft or the bearing ring, as well as various mechanical arrangements for pressing or drawing the sleeve into tight engagement.
Those skilled in the art are familiar with the operation of this type of system and the limitations of using such systems. The first limitation relates to part tolerance and the initial clearance between these parts (i.e. the shaft outside diameter, the sleeve width, the inside diameter of the bearing assembly, etc). These are inherent in every mechanical system because each component is manufactured within some tolerance range and each assembly has some initial clearances to allow the user to assemble and initially position the parts. The user can eliminate this variable by assembling the parts to an initial position or “zero reference point” that represents the position where all of these tolerances and initial clearances between the parts have been removed. This initial position can be problematical in that, if not accurately established, it can lead to further assembly problems as discussed below. None of the current mounting systems have an easy, reliable, and consistent method to determine this initial position.
Besides the tolerance and initial clearance between all of the mating parts, bearing assemblies themselves have an initial internal clearance between the internal components of the bearing. Too much, and particularly too little internal clearance, such as resulting from overloading the internal ring, can result in damage to the bearing and eventual mechanical system failure. Tapered sleeve arrangements can overload bearings, effectively reducing the internal clearance by expanding the inner ring of the bearing. The problem with current systems is that it is hard to determine exactly how much inner ring expansion might occur during the assembly process. Some systems address this issue by requiring special tooling to determine the expansion of the inner ring. However, such special tooling is not always available in the field and can be expensive.
Another limitation of tapered sleeve mounting systems relates to the manner in which the tapered sleeve is driven or drawn into engagement between the bearing assembly and the shaft. Often in these type systems, a drive thread is used to urge the tapered sleeve into place. This drive thread is often incorporated into the outside diameter of the sleeve itself, thus requiring the thread to be no less then the shaft diameter. Because these systems can be used on very large shaft diameters (e.g., 10 inches and larger), the threads themselves must also be relatively large. Consequently, special tooling is often required to torque the larger components that engage the oversized threads. Again, such special tooling is not always readily available, can be very expensive. Furthermore, this tooling does not solve the problem of accurately determining the initial position.
A second issue is that large diameter threads have larger contacting areas and thus frictional losses are increased. These forces, when combined with the frictional forces of the tapered system itself result in very large moments that must be imparted on the components to thread the sleeve properly into engagement. Also, those skilled in the art will appreciate that the frictional force in this thread can vary greatly resulting in a great deal of uncertainty in the torque required to engage this thread. This is problematic because this torque value is often used to determine the initial position and/or fully engaged position. If this torque is not consistent, the user may incorrectly believe they have reached the initial position when they have not, or they may believe they have not reached the initial position when they have. Both of these undesirable results can lead to damage to the bearing and/or mechanical system failure.
Another limitation in these mounting systems is that not only is special tooling required to install the bearing, it is also required to remove the bearing from the shaft. As discussed above, the tapered sleeve is driven into the bearing assembly using a drive mechanism that can expand the inner race of the bearing, creating a contact stress between the parts. This contact stress can be very high and requires a great deal of force to disengage the sleeve from the bearing, such as for servicing the equipment. Some mounting systems use special tooling, a hydraulic ram for instance, to overcome this force or require the user to physically overcome this force. As discussed above, this tooling can be expensive, complex to use, or may be simply unavailable in a location where the disassembly might occur.
There is a need in the art for techniques for securing rotating components, particularly bearings and shafts that alleviate or address at least some of these drawbacks of existing technology. There is a particular need for an approach in the assembly of sleeve systems that allows for accurate judgment of initial and final engagement of a sleeve between a bearing and a shaft, or between any two concentrically mating elements.